merge: use bid merge by default (BC)

In most cases merges will work exactly as before.

The only difference is in criss-cross merge situations where there is multiple
ancestors. Instead of picking an more or less arbitrary ancestor, it will
consider both ancestors and pick the best bids.

Bid merge can be disabled with --config merge.preferancestor='!'.

mercurial/merge.py

@@ -1,1151 +1,1151 b''
 # merge.py - directory-level update/merge handling for Mercurial
 #
 # Copyright 2006, 2007 Matt Mackall <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 import struct
 
 from node import nullid, nullrev, hex, bin
 from i18n import _
 from mercurial import obsolete
 import error as errormod, util, filemerge, copies, subrepo, worker, dicthelpers
 import errno, os, shutil
 
 _pack = struct.pack
 _unpack = struct.unpack
 
 def _droponode(data):
     # used for compatibility for v1
     bits = data.split("\0")
     bits = bits[:-2] + bits[-1:]
     return "\0".join(bits)
 
 class mergestate(object):
     '''track 3-way merge state of individual files
 
     it is stored on disk when needed. Two file are used, one with an old
     format, one with a new format. Both contains similar data, but the new
     format can store new kind of field.
 
     Current new format is a list of arbitrary record of the form:
 
         [type][length][content]
 
     Type is a single character, length is a 4 bytes integer, content is an
     arbitrary suites of bytes of length `length`.
 
     Type should be a letter. Capital letter are mandatory record, Mercurial
     should abort if they are unknown. lower case record can be safely ignored.
 
     Currently known record:
 
     L: the node of the "local" part of the merge (hexified version)
     O: the node of the "other" part of the merge (hexified version)
     F: a file to be merged entry
     '''
     statepathv1 = "merge/state"
     statepathv2 = "merge/state2"
 
     def __init__(self, repo):
         self._repo = repo
         self._dirty = False
         self._read()
 
     def reset(self, node=None, other=None):
         self._state = {}
         self._local = None
         self._other = None
         if node:
             self._local = node
             self._other = other
         shutil.rmtree(self._repo.join("merge"), True)
         self._dirty = False
 
     def _read(self):
         """Analyse each record content to restore a serialized state from disk
 
         This function process "record" entry produced by the de-serialization
         of on disk file.
         """
         self._state = {}
         self._local = None
         self._other = None
         records = self._readrecords()
         for rtype, record in records:
             if rtype == 'L':
                 self._local = bin(record)
             elif rtype == 'O':
                 self._other = bin(record)
             elif rtype == "F":
                 bits = record.split("\0")
                 self._state[bits[0]] = bits[1:]
             elif not rtype.islower():
                 raise util.Abort(_('unsupported merge state record: %s')
                                    % rtype)
         self._dirty = False
 
     def _readrecords(self):
         """Read merge state from disk and return a list of record (TYPE, data)
 
         We read data from both v1 and v2 files and decide which one to use.
 
         V1 has been used by version prior to 2.9.1 and contains less data than
         v2. We read both versions and check if no data in v2 contradicts
         v1. If there is not contradiction we can safely assume that both v1
         and v2 were written at the same time and use the extract data in v2. If
         there is contradiction we ignore v2 content as we assume an old version
         of Mercurial has overwritten the mergestate file and left an old v2
         file around.
 
         returns list of record [(TYPE, data), ...]"""
         v1records = self._readrecordsv1()
         v2records = self._readrecordsv2()
         oldv2 = set() # old format version of v2 record
         for rec in v2records:
             if rec[0] == 'L':
                 oldv2.add(rec)
             elif rec[0] == 'F':
                 # drop the onode data (not contained in v1)
                 oldv2.add(('F', _droponode(rec[1])))
         for rec in v1records:
             if rec not in oldv2:
                 # v1 file is newer than v2 file, use it
                 # we have to infer the "other" changeset of the merge
                 # we cannot do better than that with v1 of the format
                 mctx = self._repo[None].parents()[-1]
                 v1records.append(('O', mctx.hex()))
                 # add place holder "other" file node information
                 # nobody is using it yet so we do no need to fetch the data
                 # if mctx was wrong `mctx[bits[-2]]` may fails.
                 for idx, r in enumerate(v1records):
                     if r[0] == 'F':
                         bits = r[1].split("\0")
                         bits.insert(-2, '')
                         v1records[idx] = (r[0], "\0".join(bits))
                 return v1records
         else:
             return v2records
 
     def _readrecordsv1(self):
         """read on disk merge state for version 1 file
 
         returns list of record [(TYPE, data), ...]
 
         Note: the "F" data from this file are one entry short
               (no "other file node" entry)
         """
         records = []
         try:
             f = self._repo.opener(self.statepathv1)
             for i, l in enumerate(f):
                 if i == 0:
                     records.append(('L', l[:-1]))
                 else:
                     records.append(('F', l[:-1]))
             f.close()
         except IOError, err:
             if err.errno != errno.ENOENT:
                 raise
         return records
 
     def _readrecordsv2(self):
         """read on disk merge state for version 2 file
 
         returns list of record [(TYPE, data), ...]
         """
         records = []
         try:
             f = self._repo.opener(self.statepathv2)
             data = f.read()
             off = 0
             end = len(data)
             while off < end:
                 rtype = data[off]
                 off += 1
                 length = _unpack('>I', data[off:(off + 4)])[0]
                 off += 4
                 record = data[off:(off + length)]
                 off += length
                 records.append((rtype, record))
             f.close()
         except IOError, err:
             if err.errno != errno.ENOENT:
                 raise
         return records
 
     def active(self):
         """Whether mergestate is active.
 
         Returns True if there appears to be mergestate. This is a rough proxy
         for "is a merge in progress."
         """
         # Check local variables before looking at filesystem for performance
         # reasons.
         return bool(self._local) or bool(self._state) or \
                self._repo.opener.exists(self.statepathv1) or \
                self._repo.opener.exists(self.statepathv2)
 
     def commit(self):
         """Write current state on disk (if necessary)"""
         if self._dirty:
             records = []
             records.append(("L", hex(self._local)))
             records.append(("O", hex(self._other)))
             for d, v in self._state.iteritems():
                 records.append(("F", "\0".join([d] + v)))
             self._writerecords(records)
             self._dirty = False
 
     def _writerecords(self, records):
         """Write current state on disk (both v1 and v2)"""
         self._writerecordsv1(records)
         self._writerecordsv2(records)
 
     def _writerecordsv1(self, records):
         """Write current state on disk in a version 1 file"""
         f = self._repo.opener(self.statepathv1, "w")
         irecords = iter(records)
         lrecords = irecords.next()
         assert lrecords[0] == 'L'
         f.write(hex(self._local) + "\n")
         for rtype, data in irecords:
             if rtype == "F":
                 f.write("%s\n" % _droponode(data))
         f.close()
 
     def _writerecordsv2(self, records):
         """Write current state on disk in a version 2 file"""
         f = self._repo.opener(self.statepathv2, "w")
         for key, data in records:
             assert len(key) == 1
             format = ">sI%is" % len(data)
             f.write(_pack(format, key, len(data), data))
         f.close()
 
     def add(self, fcl, fco, fca, fd):
         """add a new (potentially?) conflicting file the merge state
         fcl: file context for local,
         fco: file context for remote,
         fca: file context for ancestors,
         fd:  file path of the resulting merge.
 
         note: also write the local version to the `.hg/merge` directory.
         """
         hash = util.sha1(fcl.path()).hexdigest()
         self._repo.opener.write("merge/" + hash, fcl.data())
         self._state[fd] = ['u', hash, fcl.path(),
                            fca.path(), hex(fca.filenode()),
                            fco.path(), hex(fco.filenode()),
                            fcl.flags()]
         self._dirty = True
 
     def __contains__(self, dfile):
         return dfile in self._state
 
     def __getitem__(self, dfile):
         return self._state[dfile][0]
 
     def __iter__(self):
         return iter(sorted(self._state))
 
     def files(self):
         return self._state.keys()
 
     def mark(self, dfile, state):
         self._state[dfile][0] = state
         self._dirty = True
 
     def unresolved(self):
         """Obtain the paths of unresolved files."""
 
         for f, entry in self._state.items():
             if entry[0] == 'u':
                 yield f
 
     def resolve(self, dfile, wctx, labels=None):
         """rerun merge process for file path `dfile`"""
         if self[dfile] == 'r':
             return 0
         stateentry = self._state[dfile]
         state, hash, lfile, afile, anode, ofile, onode, flags = stateentry
         octx = self._repo[self._other]
         fcd = wctx[dfile]
         fco = octx[ofile]
         fca = self._repo.filectx(afile, fileid=anode)
         # "premerge" x flags
         flo = fco.flags()
         fla = fca.flags()
         if 'x' in flags + flo + fla and 'l' not in flags + flo + fla:
             if fca.node() == nullid:
                 self._repo.ui.warn(_('warning: cannot merge flags for %s\n') %
                                    afile)
             elif flags == fla:
                 flags = flo
         # restore local
         f = self._repo.opener("merge/" + hash)
         self._repo.wwrite(dfile, f.read(), flags)
         f.close()
         r = filemerge.filemerge(self._repo, self._local, lfile, fcd, fco, fca,
                                 labels=labels)
         if r is None:
             # no real conflict
             del self._state[dfile]
             self._dirty = True
         elif not r:
             self.mark(dfile, 'r')
         return r
 
 def _checkunknownfile(repo, wctx, mctx, f):
     return (not repo.dirstate._ignore(f)
         and os.path.isfile(repo.wjoin(f))
         and repo.wopener.audit.check(f)
         and repo.dirstate.normalize(f) not in repo.dirstate
         and mctx[f].cmp(wctx[f]))
 
 def _checkunknown(repo, wctx, mctx):
     "check for collisions between unknown files and files in mctx"
 
     error = False
     for f in mctx:
         if f not in wctx and _checkunknownfile(repo, wctx, mctx, f):
             error = True
             wctx._repo.ui.warn(_("%s: untracked file differs\n") % f)
     if error:
         raise util.Abort(_("untracked files in working directory differ "
                            "from files in requested revision"))
 
 def _forgetremoved(wctx, mctx, branchmerge):
     """
     Forget removed files
 
     If we're jumping between revisions (as opposed to merging), and if
     neither the working directory nor the target rev has the file,
     then we need to remove it from the dirstate, to prevent the
     dirstate from listing the file when it is no longer in the
     manifest.
 
     If we're merging, and the other revision has removed a file
     that is not present in the working directory, we need to mark it
     as removed.
     """
 
     ractions = []
     factions = xactions = []
     if branchmerge:
         xactions = ractions
     for f in wctx.deleted():
         if f not in mctx:
             xactions.append((f, None, "forget deleted"))
 
     if not branchmerge:
         for f in wctx.removed():
             if f not in mctx:
                 factions.append((f, None, "forget removed"))
 
     return ractions, factions
 
 def _checkcollision(repo, wmf, actions):
     # build provisional merged manifest up
     pmmf = set(wmf)
 
     if actions:
         # k, dr, e and rd are no-op
         for m in 'a', 'f', 'g', 'cd', 'dc':
             for f, args, msg in actions[m]:
                 pmmf.add(f)
         for f, args, msg in actions['r']:
             pmmf.discard(f)
         for f, args, msg in actions['dm']:
             f2, flags = args
             pmmf.discard(f2)
             pmmf.add(f)
         for f, args, msg in actions['dg']:
             f2, flags = args
             pmmf.add(f)
         for f, args, msg in actions['m']:
             f1, f2, fa, move, anc = args
             if move:
                 pmmf.discard(f1)
             pmmf.add(f)
 
     # check case-folding collision in provisional merged manifest
     foldmap = {}
     for f in sorted(pmmf):
         fold = util.normcase(f)
         if fold in foldmap:
             raise util.Abort(_("case-folding collision between %s and %s")
                              % (f, foldmap[fold]))
         foldmap[fold] = f
 
 def manifestmerge(repo, wctx, p2, pa, branchmerge, force, partial,
                   acceptremote, followcopies):
     """
     Merge p1 and p2 with ancestor pa and generate merge action list
 
     branchmerge and force are as passed in to update
     partial = function to filter file lists
     acceptremote = accept the incoming changes without prompting
     """
 
     actions = dict((m, []) for m in 'a f g cd dc r dm dg m dr e rd k'.split())
     copy, movewithdir = {}, {}
 
     # manifests fetched in order are going to be faster, so prime the caches
     [x.manifest() for x in
      sorted(wctx.parents() + [p2, pa], key=lambda x: x.rev())]
 
     if followcopies:
         ret = copies.mergecopies(repo, wctx, p2, pa)
         copy, movewithdir, diverge, renamedelete = ret
         for of, fl in diverge.iteritems():
             actions['dr'].append((of, (fl,), "divergent renames"))
         for of, fl in renamedelete.iteritems():
             actions['rd'].append((of, (fl,), "rename and delete"))
 
     repo.ui.note(_("resolving manifests\n"))
     repo.ui.debug(" branchmerge: %s, force: %s, partial: %s\n"
                   % (bool(branchmerge), bool(force), bool(partial)))
     repo.ui.debug(" ancestor: %s, local: %s, remote: %s\n" % (pa, wctx, p2))
 
     m1, m2, ma = wctx.manifest(), p2.manifest(), pa.manifest()
     copied = set(copy.values())
     copied.update(movewithdir.values())
 
     if '.hgsubstate' in m1:
         # check whether sub state is modified
         for s in sorted(wctx.substate):
             if wctx.sub(s).dirty():
                 m1['.hgsubstate'] += "+"
                 break
 
     aborts = []
     # Compare manifests
     fdiff = dicthelpers.diff(m1, m2)
     flagsdiff = m1.flagsdiff(m2)
     diff12 = dicthelpers.join(fdiff, flagsdiff)
 
     for f, (n12, fl12) in diff12.iteritems():
         if n12:
             n1, n2 = n12
         else: # file contents didn't change, but flags did
             n1 = n2 = m1.get(f, None)
             if n1 is None:
                 # Since n1 == n2, the file isn't present in m2 either. This
                 # means that the file was removed or deleted locally and
                 # removed remotely, but that residual entries remain in flags.
                 # This can happen in manifests generated by workingctx.
                 continue
         if fl12:
             fl1, fl2 = fl12
         else: # flags didn't change, file contents did
             fl1 = fl2 = m1.flags(f)
 
         if partial and not partial(f):
             continue
         if n1 and n2:
             fa = f
             a = ma.get(f, nullid)
             if a == nullid:
                 fa = copy.get(f, f)
                 # Note: f as default is wrong - we can't really make a 3-way
                 # merge without an ancestor file.
             fla = ma.flags(fa)
             nol = 'l' not in fl1 + fl2 + fla
             if n2 == a and fl2 == fla:
                 actions['k'].append((f, (), "keep")) # remote unchanged
             elif n1 == a and fl1 == fla: # local unchanged - use remote
                 if n1 == n2: # optimization: keep local content
                     actions['e'].append((f, (fl2,), "update permissions"))
                 else:
                     actions['g'].append((f, (fl2,), "remote is newer"))
             elif nol and n2 == a: # remote only changed 'x'
                 actions['e'].append((f, (fl2,), "update permissions"))
             elif nol and n1 == a: # local only changed 'x'
                 actions['g'].append((f, (fl1,), "remote is newer"))
             else: # both changed something
                 actions['m'].append((f, (f, f, fa, False, pa.node()),
                                "versions differ"))
         elif f in copied: # files we'll deal with on m2 side
             pass
         elif n1 and f in movewithdir: # directory rename, move local
             f2 = movewithdir[f]
             actions['dm'].append((f2, (f, fl1),
                             "remote directory rename - move from " + f))
         elif n1 and f in copy:
             f2 = copy[f]
             actions['m'].append((f, (f, f2, f2, False, pa.node()),
                             "local copied/moved from " + f2))
         elif n1 and f in ma: # clean, a different, no remote
             if n1 != ma[f]:
                 if acceptremote:
                     actions['r'].append((f, None, "remote delete"))
                 else:
                     actions['cd'].append((f, None, "prompt changed/deleted"))
             elif n1[20:] == "a": # added, no remote
                 actions['f'].append((f, None, "remote deleted"))
             else:
                 actions['r'].append((f, None, "other deleted"))
         elif n2 and f in movewithdir:
             f2 = movewithdir[f]
             actions['dg'].append((f2, (f, fl2),
                             "local directory rename - get from " + f))
         elif n2 and f in copy:
             f2 = copy[f]
             if f2 in m2:
                 actions['m'].append((f, (f2, f, f2, False, pa.node()),
                                 "remote copied from " + f2))
             else:
                 actions['m'].append((f, (f2, f, f2, True, pa.node()),
                                 "remote moved from " + f2))
         elif n2 and f not in ma:
             # local unknown, remote created: the logic is described by the
             # following table:
             #
             # force  branchmerge  different  |  action
             #   n         *           n      |    get
             #   n         *           y      |   abort
             #   y         n           *      |    get
             #   y         y           n      |    get
             #   y         y           y      |   merge
             #
             # Checking whether the files are different is expensive, so we
             # don't do that when we can avoid it.
             if force and not branchmerge:
                 actions['g'].append((f, (fl2,), "remote created"))
             else:
                 different = _checkunknownfile(repo, wctx, p2, f)
                 if force and branchmerge and different:
                     # FIXME: This is wrong - f is not in ma ...
                     actions['m'].append((f, (f, f, f, False, pa.node()),
                                     "remote differs from untracked local"))
                 elif not force and different:
                     aborts.append((f, "ud"))
                 else:
                     actions['g'].append((f, (fl2,), "remote created"))
         elif n2 and n2 != ma[f]:
             different = _checkunknownfile(repo, wctx, p2, f)
             if not force and different:
                 aborts.append((f, "ud"))
             else:
                 # if different: old untracked f may be overwritten and lost
                 if acceptremote:
                     actions['g'].append((f, (m2.flags(f),),
                                    "remote recreating"))
                 else:
                     actions['dc'].append((f, (m2.flags(f),),
                                    "prompt deleted/changed"))
 
     for f, m in sorted(aborts):
         if m == "ud":
             repo.ui.warn(_("%s: untracked file differs\n") % f)
         else: assert False, m
     if aborts:
         raise util.Abort(_("untracked files in working directory differ "
                            "from files in requested revision"))
 
     if not util.checkcase(repo.path):
         # check collision between files only in p2 for clean update
         if (not branchmerge and
             (force or not wctx.dirty(missing=True, branch=False))):
             _checkcollision(repo, m2, None)
         else:
             _checkcollision(repo, m1, actions)
 
     return actions
 
 def batchremove(repo, actions):
     """apply removes to the working directory
 
     yields tuples for progress updates
     """
     verbose = repo.ui.verbose
     unlink = util.unlinkpath
     wjoin = repo.wjoin
     audit = repo.wopener.audit
     i = 0
     for f, args, msg in actions:
         repo.ui.debug(" %s: %s -> r\n" % (f, msg))
         if verbose:
             repo.ui.note(_("removing %s\n") % f)
         audit(f)
         try:
             unlink(wjoin(f), ignoremissing=True)
         except OSError, inst:
             repo.ui.warn(_("update failed to remove %s: %s!\n") %
                          (f, inst.strerror))
         if i == 100:
             yield i, f
             i = 0
         i += 1
     if i > 0:
         yield i, f
 
 def batchget(repo, mctx, actions):
     """apply gets to the working directory
 
     mctx is the context to get from
 
     yields tuples for progress updates
     """
     verbose = repo.ui.verbose
     fctx = mctx.filectx
     wwrite = repo.wwrite
     i = 0
     for f, args, msg in actions:
         repo.ui.debug(" %s: %s -> g\n" % (f, msg))
         if verbose:
             repo.ui.note(_("getting %s\n") % f)
         wwrite(f, fctx(f).data(), args[0])
         if i == 100:
             yield i, f
             i = 0
         i += 1
     if i > 0:
         yield i, f
 
 def applyupdates(repo, actions, wctx, mctx, overwrite, labels=None):
     """apply the merge action list to the working directory
 
     wctx is the working copy context
     mctx is the context to be merged into the working copy
 
     Return a tuple of counts (updated, merged, removed, unresolved) that
     describes how many files were affected by the update.
     """
 
     updated, merged, removed, unresolved = 0, 0, 0, 0
     ms = mergestate(repo)
     ms.reset(wctx.p1().node(), mctx.node())
     moves = []
     for m, l in actions.items():
         l.sort()
 
     # prescan for merges
     for f, args, msg in actions['m']:
         f1, f2, fa, move, anc = args
         if f == '.hgsubstate': # merged internally
             continue
         repo.ui.debug(" preserving %s for resolve of %s\n" % (f1, f))
         fcl = wctx[f1]
         fco = mctx[f2]
         actx = repo[anc]
         if fa in actx:
             fca = actx[fa]
         else:
             fca = repo.filectx(f1, fileid=nullrev)
         ms.add(fcl, fco, fca, f)
         if f1 != f and move:
             moves.append(f1)
 
     audit = repo.wopener.audit
     _updating = _('updating')
     _files = _('files')
     progress = repo.ui.progress
 
     # remove renamed files after safely stored
     for f in moves:
         if os.path.lexists(repo.wjoin(f)):
             repo.ui.debug("removing %s\n" % f)
             audit(f)
             util.unlinkpath(repo.wjoin(f))
 
     numupdates = sum(len(l) for m, l in actions.items() if m != 'k')
 
     if [a for a in actions['r'] if a[0] == '.hgsubstate']:
         subrepo.submerge(repo, wctx, mctx, wctx, overwrite)
 
     # remove in parallel (must come first)
     z = 0
     prog = worker.worker(repo.ui, 0.001, batchremove, (repo,), actions['r'])
     for i, item in prog:
         z += i
         progress(_updating, z, item=item, total=numupdates, unit=_files)
     removed = len(actions['r'])
 
     # get in parallel
     prog = worker.worker(repo.ui, 0.001, batchget, (repo, mctx), actions['g'])
     for i, item in prog:
         z += i
         progress(_updating, z, item=item, total=numupdates, unit=_files)
     updated = len(actions['g'])
 
     if [a for a in actions['g'] if a[0] == '.hgsubstate']:
         subrepo.submerge(repo, wctx, mctx, wctx, overwrite)
 
     # forget (manifest only, just log it) (must come first)
     for f, args, msg in actions['f']:
         repo.ui.debug(" %s: %s -> f\n" % (f, msg))
         z += 1
         progress(_updating, z, item=f, total=numupdates, unit=_files)
 
     # re-add (manifest only, just log it)
     for f, args, msg in actions['a']:
         repo.ui.debug(" %s: %s -> a\n" % (f, msg))
         z += 1
         progress(_updating, z, item=f, total=numupdates, unit=_files)
 
     # keep (noop, just log it)
     for f, args, msg in actions['k']:
         repo.ui.debug(" %s: %s -> k\n" % (f, msg))
         # no progress
 
     # merge
     for f, args, msg in actions['m']:
         repo.ui.debug(" %s: %s -> m\n" % (f, msg))
         z += 1
         progress(_updating, z, item=f, total=numupdates, unit=_files)
         f1, f2, fa, move, anc = args
         if f == '.hgsubstate': # subrepo states need updating
             subrepo.submerge(repo, wctx, mctx, wctx.ancestor(mctx),
                              overwrite)
             continue
         audit(f)
         r = ms.resolve(f, wctx, labels=labels)
         if r is not None and r > 0:
             unresolved += 1
         else:
             if r is None:
                 updated += 1
             else:
                 merged += 1
 
     # directory rename, move local
     for f, args, msg in actions['dm']:
         repo.ui.debug(" %s: %s -> dm\n" % (f, msg))
         z += 1
         progress(_updating, z, item=f, total=numupdates, unit=_files)
         f0, flags = args
         repo.ui.note(_("moving %s to %s\n") % (f0, f))
         audit(f)
         repo.wwrite(f, wctx.filectx(f0).data(), flags)
         util.unlinkpath(repo.wjoin(f0))
         updated += 1
 
     # local directory rename, get
     for f, args, msg in actions['dg']:
         repo.ui.debug(" %s: %s -> dg\n" % (f, msg))
         z += 1
         progress(_updating, z, item=f, total=numupdates, unit=_files)
         f0, flags = args
         repo.ui.note(_("getting %s to %s\n") % (f0, f))
         repo.wwrite(f, mctx.filectx(f0).data(), flags)
         updated += 1
 
     # divergent renames
     for f, args, msg in actions['dr']:
         repo.ui.debug(" %s: %s -> dr\n" % (f, msg))
         z += 1
         progress(_updating, z, item=f, total=numupdates, unit=_files)
         fl, = args
         repo.ui.warn(_("note: possible conflict - %s was renamed "
                        "multiple times to:\n") % f)
         for nf in fl:
             repo.ui.warn(" %s\n" % nf)
 
     # rename and delete
     for f, args, msg in actions['rd']:
         repo.ui.debug(" %s: %s -> rd\n" % (f, msg))
         z += 1
         progress(_updating, z, item=f, total=numupdates, unit=_files)
         fl, = args
         repo.ui.warn(_("note: possible conflict - %s was deleted "
                        "and renamed to:\n") % f)
         for nf in fl:
             repo.ui.warn(" %s\n" % nf)
 
     # exec
     for f, args, msg in actions['e']:
         repo.ui.debug(" %s: %s -> e\n" % (f, msg))
         z += 1
         progress(_updating, z, item=f, total=numupdates, unit=_files)
         flags, = args
         audit(f)
         util.setflags(repo.wjoin(f), 'l' in flags, 'x' in flags)
         updated += 1
 
     ms.commit()
     progress(_updating, None, total=numupdates, unit=_files)
 
     return updated, merged, removed, unresolved
 
 def calculateupdates(repo, wctx, mctx, ancestors, branchmerge, force, partial,
                      acceptremote, followcopies):
     "Calculate the actions needed to merge mctx into wctx using ancestors"
 
     if len(ancestors) == 1: # default
         actions = manifestmerge(repo, wctx, mctx, ancestors[0],
                                 branchmerge, force,
                                 partial, acceptremote, followcopies)
 
-    else: # only when merge.preferancestor=* - experimentalish code
+    else: # only when merge.preferancestor=* - the default
         repo.ui.status(
             _("note: merging %s and %s using bids from ancestors %s\n") %
             (wctx, mctx, _(' and ').join(str(anc) for anc in ancestors)))
 
         # Call for bids
         fbids = {} # mapping filename to bids (action method to list af actions)
         for ancestor in ancestors:
             repo.ui.note(_('\ncalculating bids for ancestor %s\n') % ancestor)
             actions = manifestmerge(repo, wctx, mctx, ancestor,
                                     branchmerge, force,
                                     partial, acceptremote, followcopies)
             for m, l in sorted(actions.items()):
                 for a in l:
                     f, args, msg = a
                     repo.ui.debug(' %s: %s -> %s\n' % (f, msg, m))
                     if f in fbids:
                         d = fbids[f]
                         if m in d:
                             d[m].append(a)
                         else:
                             d[m] = [a]
                     else:
                         fbids[f] = {m: [a]}
 
         # Pick the best bid for each file
         repo.ui.note(_('\nauction for merging merge bids\n'))
         actions = dict((m, []) for m in actions.keys())
         for f, bids in sorted(fbids.items()):
             # bids is a mapping from action method to list af actions
             # Consensus?
             if len(bids) == 1: # all bids are the same kind of method
                 m, l = bids.items()[0]
                 if util.all(a == l[0] for a in l[1:]): # len(bids) is > 1
                     repo.ui.note(" %s: consensus for %s\n" % (f, m))
                     actions[m].append(l[0])
                     continue
             # If keep is an option, just do it.
             if "k" in bids:
                 repo.ui.note(" %s: picking 'keep' action\n" % f)
                 actions['k'].append(bids["k"][0])
                 continue
             # If there are gets and they all agree [how could they not?], do it.
             if "g" in bids:
                 ga0 = bids["g"][0]
                 if util.all(a == ga0 for a in bids["g"][1:]):
                     repo.ui.note(" %s: picking 'get' action\n" % f)
                     actions['g'].append(ga0)
                     continue
             # TODO: Consider other simple actions such as mode changes
             # Handle inefficient democrazy.
             repo.ui.note(_(' %s: multiple bids for merge action:\n') % f)
             for m, l in sorted(bids.items()):
                 for _f, args, msg in l:
                     repo.ui.note('  %s -> %s\n' % (msg, m))
             # Pick random action. TODO: Instead, prompt user when resolving
             m, l = bids.items()[0]
             repo.ui.warn(_(' %s: ambiguous merge - picked %s action\n') %
                          (f, m))
             actions[m].append(l[0])
             continue
         repo.ui.note(_('end of auction\n\n'))
 
     # Prompt and create actions. TODO: Move this towards resolve phase.
     for f, args, msg in actions['cd']:
         if repo.ui.promptchoice(
             _("local changed %s which remote deleted\n"
               "use (c)hanged version or (d)elete?"
               "$$ &Changed $$ &Delete") % f, 0):
             actions['r'].append((f, None, "prompt delete"))
         else:
             actions['a'].append((f, None, "prompt keep"))
     del actions['cd'][:]
 
     for f, args, msg in actions['dc']:
         flags, = args
         if repo.ui.promptchoice(
             _("remote changed %s which local deleted\n"
               "use (c)hanged version or leave (d)eleted?"
               "$$ &Changed $$ &Deleted") % f, 0) == 0:
             actions['g'].append((f, (flags,), "prompt recreating"))
     del actions['dc'][:]
 
     if wctx.rev() is None:
         ractions, factions = _forgetremoved(wctx, mctx, branchmerge)
         actions['r'].extend(ractions)
         actions['f'].extend(factions)
 
     return actions
 
 def recordupdates(repo, actions, branchmerge):
     "record merge actions to the dirstate"
     # remove (must come first)
     for f, args, msg in actions['r']:
         if branchmerge:
             repo.dirstate.remove(f)
         else:
             repo.dirstate.drop(f)
 
     # forget (must come first)
     for f, args, msg in actions['f']:
         repo.dirstate.drop(f)
 
     # re-add
     for f, args, msg in actions['a']:
         if not branchmerge:
             repo.dirstate.add(f)
 
     # exec change
     for f, args, msg in actions['e']:
         repo.dirstate.normallookup(f)
 
     # keep
     for f, args, msg in actions['k']:
         pass
 
     # get
     for f, args, msg in actions['g']:
         if branchmerge:
             repo.dirstate.otherparent(f)
         else:
             repo.dirstate.normal(f)
 
     # merge
     for f, args, msg in actions['m']:
         f1, f2, fa, move, anc = args
         if branchmerge:
             # We've done a branch merge, mark this file as merged
             # so that we properly record the merger later
             repo.dirstate.merge(f)
             if f1 != f2: # copy/rename
                 if move:
                     repo.dirstate.remove(f1)
                 if f1 != f:
                     repo.dirstate.copy(f1, f)
                 else:
                     repo.dirstate.copy(f2, f)
         else:
             # We've update-merged a locally modified file, so
             # we set the dirstate to emulate a normal checkout
             # of that file some time in the past. Thus our
             # merge will appear as a normal local file
             # modification.
             if f2 == f: # file not locally copied/moved
                 repo.dirstate.normallookup(f)
             if move:
                 repo.dirstate.drop(f1)
 
     # directory rename, move local
     for f, args, msg in actions['dm']:
         f0, flag = args
         if f0 not in repo.dirstate:
             # untracked file moved
             continue
         if branchmerge:
             repo.dirstate.add(f)
             repo.dirstate.remove(f0)
             repo.dirstate.copy(f0, f)
         else:
             repo.dirstate.normal(f)
             repo.dirstate.drop(f0)
 
     # directory rename, get
     for f, args, msg in actions['dg']:
         f0, flag = args
         if branchmerge:
             repo.dirstate.add(f)
             repo.dirstate.copy(f0, f)
         else:
             repo.dirstate.normal(f)
 
 def update(repo, node, branchmerge, force, partial, ancestor=None,
            mergeancestor=False, labels=None):
     """
     Perform a merge between the working directory and the given node
 
     node = the node to update to, or None if unspecified
     branchmerge = whether to merge between branches
     force = whether to force branch merging or file overwriting
     partial = a function to filter file lists (dirstate not updated)
     mergeancestor = whether it is merging with an ancestor. If true,
       we should accept the incoming changes for any prompts that occur.
       If false, merging with an ancestor (fast-forward) is only allowed
       between different named branches. This flag is used by rebase extension
       as a temporary fix and should be avoided in general.
 
     The table below shows all the behaviors of the update command
     given the -c and -C or no options, whether the working directory
     is dirty, whether a revision is specified, and the relationship of
     the parent rev to the target rev (linear, on the same named
     branch, or on another named branch).
 
     This logic is tested by test-update-branches.t.
 
     -c  -C  dirty  rev  |  linear   same  cross
      n   n    n     n   |    ok     (1)     x
      n   n    n     y   |    ok     ok     ok
      n   n    y     n   |   merge   (2)    (2)
      n   n    y     y   |   merge   (3)    (3)
      n   y    *     *   |    ---  discard  ---
      y   n    y     *   |    ---    (4)    ---
      y   n    n     *   |    ---    ok     ---
      y   y    *     *   |    ---    (5)    ---
 
     x = can't happen
     * = don't-care
     1 = abort: not a linear update (merge or update --check to force update)
     2 = abort: uncommitted changes (commit and merge, or update --clean to
                  discard changes)
     3 = abort: uncommitted changes (commit or update --clean to discard changes)
     4 = abort: uncommitted changes (checked in commands.py)
     5 = incompatible options (checked in commands.py)
 
     Return the same tuple as applyupdates().
     """
 
     onode = node
     wlock = repo.wlock()
     try:
         wc = repo[None]
         pl = wc.parents()
         p1 = pl[0]
         pas = [None]
         if ancestor:
             pas = [repo[ancestor]]
 
         if node is None:
             # Here is where we should consider bookmarks, divergent bookmarks,
             # foreground changesets (successors), and tip of current branch;
             # but currently we are only checking the branch tips.
             try:
                 node = repo.branchtip(wc.branch())
             except errormod.RepoLookupError:
                 if wc.branch() == "default": # no default branch!
                     node = repo.lookup("tip") # update to tip
                 else:
                     raise util.Abort(_("branch %s not found") % wc.branch())
 
             if p1.obsolete() and not p1.children():
                 # allow updating to successors
                 successors = obsolete.successorssets(repo, p1.node())
 
                 # behavior of certain cases is as follows,
                 #
                 # divergent changesets: update to highest rev, similar to what
                 #     is currently done when there are more than one head
                 #     (i.e. 'tip')
                 #
                 # replaced changesets: same as divergent except we know there
                 # is no conflict
                 #
                 # pruned changeset: no update is done; though, we could
                 #     consider updating to the first non-obsolete parent,
                 #     similar to what is current done for 'hg prune'
 
                 if successors:
                     # flatten the list here handles both divergent (len > 1)
                     # and the usual case (len = 1)
                     successors = [n for sub in successors for n in sub]
 
                     # get the max revision for the given successors set,
                     # i.e. the 'tip' of a set
                     node = repo.revs("max(%ln)", successors)[0]
                     pas = [p1]
 
         overwrite = force and not branchmerge
 
         p2 = repo[node]
         if pas[0] is None:
-            if repo.ui.config("merge", "preferancestor") == '*':
+            if repo.ui.config("merge", "preferancestor", '*') == '*':
                 cahs = repo.changelog.commonancestorsheads(p1.node(), p2.node())
                 pas = [repo[anc] for anc in (sorted(cahs) or [nullid])]
             else:
                 pas = [p1.ancestor(p2, warn=branchmerge)]
 
         fp1, fp2, xp1, xp2 = p1.node(), p2.node(), str(p1), str(p2)
 
         ### check phase
         if not overwrite and len(pl) > 1:
             raise util.Abort(_("outstanding uncommitted merges"))
         if branchmerge:
             if pas == [p2]:
                 raise util.Abort(_("merging with a working directory ancestor"
                                    " has no effect"))
             elif pas == [p1]:
                 if not mergeancestor and p1.branch() == p2.branch():
                     raise util.Abort(_("nothing to merge"),
                                      hint=_("use 'hg update' "
                                             "or check 'hg heads'"))
             if not force and (wc.files() or wc.deleted()):
                 raise util.Abort(_("uncommitted changes"),
                                  hint=_("use 'hg status' to list changes"))
             for s in sorted(wc.substate):
                 if wc.sub(s).dirty():
                     raise util.Abort(_("uncommitted changes in "
                                        "subrepository '%s'") % s)
 
         elif not overwrite:
             if p1 == p2: # no-op update
                 # call the hooks and exit early
                 repo.hook('preupdate', throw=True, parent1=xp2, parent2='')
                 repo.hook('update', parent1=xp2, parent2='', error=0)
                 return 0, 0, 0, 0
 
             if pas not in ([p1], [p2]):  # nonlinear
                 dirty = wc.dirty(missing=True)
                 if dirty or onode is None:
                     # Branching is a bit strange to ensure we do the minimal
                     # amount of call to obsolete.background.
                     foreground = obsolete.foreground(repo, [p1.node()])
                     # note: the <node> variable contains a random identifier
                     if repo[node].node() in foreground:
                         pas = [p1]  # allow updating to successors
                     elif dirty:
                         msg = _("uncommitted changes")
                         if onode is None:
                             hint = _("commit and merge, or update --clean to"
                                      " discard changes")
                         else:
                             hint = _("commit or update --clean to discard"
                                      " changes")
                         raise util.Abort(msg, hint=hint)
                     else:  # node is none
                         msg = _("not a linear update")
                         hint = _("merge or update --check to force update")
                         raise util.Abort(msg, hint=hint)
                 else:
                     # Allow jumping branches if clean and specific rev given
                     pas = [p1]
 
         followcopies = False
         if overwrite:
             pas = [wc]
         elif pas == [p2]: # backwards
             pas = [wc.p1()]
         elif not branchmerge and not wc.dirty(missing=True):
             pass
         elif pas[0] and repo.ui.configbool("merge", "followcopies", True):
             followcopies = True
 
         ### calculate phase
         actions = calculateupdates(repo, wc, p2, pas, branchmerge, force,
                                    partial, mergeancestor, followcopies)
 
         ### apply phase
         if not branchmerge: # just jump to the new rev
             fp1, fp2, xp1, xp2 = fp2, nullid, xp2, ''
         if not partial:
             repo.hook('preupdate', throw=True, parent1=xp1, parent2=xp2)
             # note that we're in the middle of an update
             repo.vfs.write('updatestate', p2.hex())
 
         stats = applyupdates(repo, actions, wc, p2, overwrite, labels=labels)
 
         if not partial:
             repo.dirstate.beginparentchange()
             repo.setparents(fp1, fp2)
             recordupdates(repo, actions, branchmerge)
             # update completed, clear state
             util.unlink(repo.join('updatestate'))
 
             if not branchmerge:
                 repo.dirstate.setbranch(p2.branch())
             repo.dirstate.endparentchange()
     finally:
         wlock.release()
 
     if not partial:
         repo.hook('update', parent1=xp1, parent2=xp2, error=stats[3])
     return stats

tests/test-merge-criss-cross.t

@@ -1,355 +1,355 b''
 Criss cross merging
 
   $ hg init criss-cross
   $ cd criss-cross
   $ echo '0 base' > f1
   $ echo '0 base' > f2
   $ hg ci -Aqm '0 base'
 
   $ echo '1 first change' > f1
   $ hg ci -m '1 first change f1'
 
   $ hg up -qr0
   $ echo '2 first change' > f2
   $ hg ci -qm '2 first change f2'
 
   $ hg merge -qr 1
   $ hg ci -m '3 merge'
 
   $ hg up -qr2
   $ hg merge -qr1
   $ hg ci -qm '4 merge'
 
   $ echo '5 second change' > f1
   $ hg ci -m '5 second change f1'
 
   $ hg up -r3
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
   $ echo '6 second change' > f2
   $ hg ci -m '6 second change f2'
 
   $ hg log -G
   @  changeset:   6:3b08d01b0ab5
   |  tag:         tip
   |  parent:      3:cf89f02107e5
   |  user:        test
   |  date:        Thu Jan 01 00:00:00 1970 +0000
   |  summary:     6 second change f2
   |
   | o  changeset:   5:adfe50279922
   | |  user:        test
   | |  date:        Thu Jan 01 00:00:00 1970 +0000
   | |  summary:     5 second change f1
   | |
   | o    changeset:   4:7d3e55501ae6
   | |\   parent:      2:40663881a6dd
   | | |  parent:      1:0f6b37dbe527
   | | |  user:        test
   | | |  date:        Thu Jan 01 00:00:00 1970 +0000
   | | |  summary:     4 merge
   | | |
   o---+  changeset:   3:cf89f02107e5
   | | |  parent:      2:40663881a6dd
   |/ /   parent:      1:0f6b37dbe527
   | |    user:        test
   | |    date:        Thu Jan 01 00:00:00 1970 +0000
   | |    summary:     3 merge
   | |
   | o  changeset:   2:40663881a6dd
   | |  parent:      0:40494bf2444c
   | |  user:        test
   | |  date:        Thu Jan 01 00:00:00 1970 +0000
   | |  summary:     2 first change f2
   | |
   o |  changeset:   1:0f6b37dbe527
   |/   user:        test
   |    date:        Thu Jan 01 00:00:00 1970 +0000
   |    summary:     1 first change f1
   |
   o  changeset:   0:40494bf2444c
      user:        test
      date:        Thu Jan 01 00:00:00 1970 +0000
      summary:     0 base
   
 
-  $ hg merge -v --debug --tool internal:dump 5
+  $ hg merge -v --debug --tool internal:dump 5 --config merge.preferancestor='!'
   note: using 0f6b37dbe527 as ancestor of 3b08d01b0ab5 and adfe50279922
         alternatively, use --config merge.preferancestor=40663881a6dd
     searching for copies back to rev 3
   resolving manifests
    branchmerge: True, force: False, partial: False
    ancestor: 0f6b37dbe527, local: 3b08d01b0ab5+, remote: adfe50279922
    preserving f2 for resolve of f2
    f1: remote is newer -> g
   getting f1
   updating: f1 1/2 files (50.00%)
    f2: versions differ -> m
   updating: f2 2/2 files (100.00%)
   picked tool 'internal:dump' for f2 (binary False symlink False)
   merging f2
   my f2@3b08d01b0ab5+ other f2@adfe50279922 ancestor f2@40494bf2444c
   1 files updated, 0 files merged, 0 files removed, 1 files unresolved
   use 'hg resolve' to retry unresolved file merges or 'hg update -C .' to abandon
   [1]
 
   $ head *
   ==> f1 <==
   5 second change
   
   ==> f2 <==
   6 second change
   
   ==> f2.base <==
   0 base
   
   ==> f2.local <==
   6 second change
   
   ==> f2.orig <==
   6 second change
   
   ==> f2.other <==
   2 first change
 
   $ hg up -qC .
   $ hg merge -v --tool internal:dump 5 --config merge.preferancestor="null 40663881 3b08d"
   note: using 40663881a6dd as ancestor of 3b08d01b0ab5 and adfe50279922
         alternatively, use --config merge.preferancestor=0f6b37dbe527
   resolving manifests
   merging f1
   0 files updated, 0 files merged, 0 files removed, 1 files unresolved
   use 'hg resolve' to retry unresolved file merges or 'hg update -C .' to abandon
   [1]
 
 Redo merge with merge.preferancestor="*" to enable bid merge
 
   $ rm f*
   $ hg up -qC .
   $ hg merge -v --debug --tool internal:dump 5 --config merge.preferancestor="*"
   note: merging 3b08d01b0ab5+ and adfe50279922 using bids from ancestors 0f6b37dbe527 and 40663881a6dd
   
   calculating bids for ancestor 0f6b37dbe527
     searching for copies back to rev 3
   resolving manifests
    branchmerge: True, force: False, partial: False
    ancestor: 0f6b37dbe527, local: 3b08d01b0ab5+, remote: adfe50279922
    f1: remote is newer -> g
    f2: versions differ -> m
   
   calculating bids for ancestor 40663881a6dd
     searching for copies back to rev 3
   resolving manifests
    branchmerge: True, force: False, partial: False
    ancestor: 40663881a6dd, local: 3b08d01b0ab5+, remote: adfe50279922
    f2: keep -> k
    f1: versions differ -> m
   
   auction for merging merge bids
    f1: picking 'get' action
    f2: picking 'keep' action
   end of auction
   
    f1: remote is newer -> g
   getting f1
   updating: f1 1/1 files (100.00%)
    f2: keep -> k
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
   (branch merge, don't forget to commit)
 
   $ head *
   ==> f1 <==
   5 second change
   
   ==> f2 <==
   6 second change
 
 
 The other way around:
 
   $ hg up -C -r5
   2 files updated, 0 files merged, 0 files removed, 0 files unresolved
   $ hg merge -v --debug --config merge.preferancestor="*"
   note: merging adfe50279922+ and 3b08d01b0ab5 using bids from ancestors 0f6b37dbe527 and 40663881a6dd
   
   calculating bids for ancestor 0f6b37dbe527
     searching for copies back to rev 3
   resolving manifests
    branchmerge: True, force: False, partial: False
    ancestor: 0f6b37dbe527, local: adfe50279922+, remote: 3b08d01b0ab5
    f1: keep -> k
    f2: versions differ -> m
   
   calculating bids for ancestor 40663881a6dd
     searching for copies back to rev 3
   resolving manifests
    branchmerge: True, force: False, partial: False
    ancestor: 40663881a6dd, local: adfe50279922+, remote: 3b08d01b0ab5
    f2: remote is newer -> g
    f1: versions differ -> m
   
   auction for merging merge bids
    f1: picking 'keep' action
    f2: picking 'get' action
   end of auction
   
    f2: remote is newer -> g
   getting f2
   updating: f2 1/1 files (100.00%)
    f1: keep -> k
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
   (branch merge, don't forget to commit)
 
   $ head *
   ==> f1 <==
   5 second change
   
   ==> f2 <==
   6 second change
 
 Verify how the output looks and and how verbose it is:
 
   $ hg up -qC
-  $ hg merge --config merge.preferancestor="*"
+  $ hg merge
   note: merging 3b08d01b0ab5+ and adfe50279922 using bids from ancestors 0f6b37dbe527 and 40663881a6dd
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
   (branch merge, don't forget to commit)
 
   $ hg up -qC
-  $ hg merge -v --config merge.preferancestor="*"
+  $ hg merge -v
   note: merging 3b08d01b0ab5+ and adfe50279922 using bids from ancestors 0f6b37dbe527 and 40663881a6dd
   
   calculating bids for ancestor 0f6b37dbe527
   resolving manifests
   
   calculating bids for ancestor 40663881a6dd
   resolving manifests
   
   auction for merging merge bids
    f1: picking 'get' action
    f2: picking 'keep' action
   end of auction
   
   getting f1
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
   (branch merge, don't forget to commit)
 
   $ hg up -qC
   $ hg merge -v --debug --config merge.preferancestor="*"
   note: merging 3b08d01b0ab5+ and adfe50279922 using bids from ancestors 0f6b37dbe527 and 40663881a6dd
   
   calculating bids for ancestor 0f6b37dbe527
     searching for copies back to rev 3
   resolving manifests
    branchmerge: True, force: False, partial: False
    ancestor: 0f6b37dbe527, local: 3b08d01b0ab5+, remote: adfe50279922
    f1: remote is newer -> g
    f2: versions differ -> m
   
   calculating bids for ancestor 40663881a6dd
     searching for copies back to rev 3
   resolving manifests
    branchmerge: True, force: False, partial: False
    ancestor: 40663881a6dd, local: 3b08d01b0ab5+, remote: adfe50279922
    f2: keep -> k
    f1: versions differ -> m
   
   auction for merging merge bids
    f1: picking 'get' action
    f2: picking 'keep' action
   end of auction
   
    f1: remote is newer -> g
   getting f1
   updating: f1 1/1 files (100.00%)
    f2: keep -> k
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
   (branch merge, don't forget to commit)
 
   $ cd ..
 
 http://stackoverflow.com/questions/9350005/how-do-i-specify-a-merge-base-to-use-in-a-hg-merge/9430810
 
   $ hg init ancestor-merging
   $ cd ancestor-merging
   $ echo a > x
   $ hg commit -A -m a x
   $ hg update -q 0
   $ echo b >> x
   $ hg commit -m b
   $ hg update -q 0
   $ echo c >> x
   $ hg commit -qm c
   $ hg update -q 1
   $ hg merge -q --tool internal:local 2
   $ echo c >> x
   $ hg commit -m bc
   $ hg update -q 2
   $ hg merge -q --tool internal:local 1
   $ echo b >> x
   $ hg commit -qm cb
 
-  $ hg merge
+  $ hg merge --config merge.preferancestor='!'
   note: using 70008a2163f6 as ancestor of 0d355fdef312 and 4b8b546a3eef
         alternatively, use --config merge.preferancestor=b211bbc6eb3c
   merging x
   0 files updated, 1 files merged, 0 files removed, 0 files unresolved
   (branch merge, don't forget to commit)
   $ cat x
   a
   c
   b
   c
 
   $ hg up -qC .
 
   $ hg merge --config merge.preferancestor=b211bbc6eb3c
   note: using b211bbc6eb3c as ancestor of 0d355fdef312 and 4b8b546a3eef
         alternatively, use --config merge.preferancestor=70008a2163f6
   merging x
   0 files updated, 1 files merged, 0 files removed, 0 files unresolved
   (branch merge, don't forget to commit)
   $ cat x
   a
   b
   c
   b
 
   $ hg up -qC .
 
   $ hg merge -v --config merge.preferancestor="*"
   note: merging 0d355fdef312+ and 4b8b546a3eef using bids from ancestors 70008a2163f6 and b211bbc6eb3c
   
   calculating bids for ancestor 70008a2163f6
   resolving manifests
   
   calculating bids for ancestor b211bbc6eb3c
   resolving manifests
   
   auction for merging merge bids
    x: multiple bids for merge action:
     versions differ -> m
     versions differ -> m
    x: ambiguous merge - picked m action
   end of auction
   
   merging x
   0 files updated, 1 files merged, 0 files removed, 0 files unresolved
   (branch merge, don't forget to commit)
   $ cat x
   a
   c
   b
   c
 
 Verify that the old context ancestor works with / despite preferancestor:
 
   $ hg log -r 'ancestor(head())' --config merge.preferancestor=1 -T '{rev}\n'
   1
   $ hg log -r 'ancestor(head())' --config merge.preferancestor=2 -T '{rev}\n'
   2
   $ hg log -r 'ancestor(head())' --config merge.preferancestor=3 -T '{rev}\n'
   1
   $ hg log -r 'ancestor(head())' --config merge.preferancestor='1337 * - 2' -T '{rev}\n'
   2
 
   $ cd ..